Manufacture of ferrous picrate and additives containing same

ABSTRACT

A process for preparing ferrous picrate is disclosed. The process includes the step of reacting under substantially non-oxidising conditions ferrous carbonate substantially free from ferric compounds with a substantially water-free solution of picric acid in a solvent medium to produce a solution of ferric picrate. The solvent medium is selected from aromatic hydrocarbon solvents, mixtures of aromatic hydrocarbon solvents, straight- or branched-chain aliphatic alcohols, mixtures of straight or branched-chain aliphatic alcohols, and mixtures of straight- or branched-chain aliphatic alcohols and aromatic hydrocarbon solvents. The reaction is preferably carried out under a continuously maintained inert atmosphere and at a temperature between 10° C. and 120° C.

This application is a 371 of PCT/AU94/00259, filed May 19, 1994.

BACKGROUND OF THE INVENTION

The present invention relates to the manufacture of ferrous picrate.

It has been suggested that the addition of ferrous picrate tocarbonaceous fuel results in improvement to the combustion of the fuel.Both ferrous picrate and picric acid are to some extent explosive whenin the dry state, necessitating precautions in their use and transport.Ferrous picrate in the dry state is also readily oxidised to ferricpicrate in air. Ferric compounds are ineffective as combustionimprovers.

In Australian Patent No. 621243 there is disclosed a process forpreparing ferrous picrate comprising reacting picric acid in solution ina straight- or branched-chain aliphatic alcohol with iron carbonyl at atemperature between 10° C. and 120° C. Also disclosed is a liquidadditive comprising ferrous picrate prepared by the process described,picric acid, an aromatic solvent, and a straight- or branched-chainaliphatic alcohol.

In Australian Patent No. 624964 there is disclosed a process forpreparing ferrous picrate comprising reacting under a continuouslymaintained inert atmosphere an aqueous solution of a ferrous salt withan alkali hydroxide to produce a ferrous hydroxide precipitate, removingwater and by-products from the ferrous hydroxide, adding the ferroushydroxide and a straight or branched-chain aliphatic alcohol to awater-free solution of picric acid in an aromatic solvent, and removingany insoluble material from the solution. Also disclosed is a liquidadditive comprising ferrous picrate prepared by a process as described,an aromatic solvent, an aromatic nitro compound and a straight- orbranched-chain aliphatic alcohol.

In Example 5 of U.S. Pat. No. 3,282,858, a method of manufacture offerrous picrate is disclosed which comprises reacting ferrous sulphatewith sodium carbonate to produce a ferrous carbonate precepitate whichis then dissolved in alcohol and reacted with picric acid to produceferrous picrate. The ferrous picrate crystals are separated from theliquid in which they are made, and taken up in solvents to provide afuel additive. No attempt is made to exclude oxygen from the ferrouscarbonate solution or the solid ferrous picrate, but hydroquinone isadded to the reaction mixture to minimise the oxidation of ferrouscompounds.

SUMMARY OF THE INVENTION

One object of the present invention is to provide in one embodiment aprocess for preparing ferrous picrate for subsequent use as a fueladditive whereby the use of materials in a hazardous state is avoided,and whereby the presence of ferric compounds is minimised.

Accordingly, in one embodiment the present invention provides a processfor preparing ferrous picrate comprising reacting under an inertatmosphere ferrous carbonate substantially free from ferric compoundswith a solution of substantially water-free picric acid in a solventmedium selected from an aromatic hydrocarbon solvent, a mixture ofaromatic hydrocarbon solvents, a straight- or branched-chain aliphaticalcohol, mixtures of straight- and/or branched-chain aliphatic alcohols,and a mixture of straight- and/or branched-chain aliphatic alcohols witharomatic hydrocarbon solvents, to produce a solution of ferrous picrate.

In another embodiment, the present invention provides a process forpreparing ferrous picrate comprising reacting under an inert atmosphereferrous carbonate substantially free from ferric compounds with asubstantially water-free solution of picric acid in a solvent mediumselected from an aromatic hydrocarbon solvent, a mixture of aromatichydrocarbon solvents, a straight- or a branched-chain aliphatic alcohol,a mixture of straight- and/or branched-chain aliphatic alcohols, and amixture of straight- and/or branched-chain aliphatic alcohols witharomatic hydrocarbon solvents and at a temperature between 10° C. and120° C., to produce a solution of ferrous picrate.

We have now surprisingly found in one particularly preferred embodimentof the invention that by reacting ferrous carbonate which issubstantially free from ferric compounds with picric add under an inertatmosphere, without adding hydroquinone, and maintaining the ferrouspicrate and the picric acid always in solution, we can obtain a ferrouspicrate product that is more effective in promoting the completecombustion of carbonaceous fuel than is the ferrous picrate productproduced by the process of Example 5 of U.S. Pat. No. 3,282,858. Inaddition, hazards which would arise from dry ferrous picrate and drypicric acid are avoided.

The process of the present invention also provides a viable alternativeto the process disclosed in, for example, Australian Patent No. 621243when a source of iron carbonyl is otherwise unavailable, or for healthreasons the use of iron carbonyl, which is a toxic compound, isconsidered unsafe.

The reaction is preferably carried out under a continuously maintainedinert atmosphere eg. nitrogen to achieve a substantially non-oxidisingreaction condition.

The ferrous carbonate is preferably prepared by reacting in solutionferrous sulphate with sodium carbonate and removing aqueous liquid undera continuously maintained inert atmosphere. The preferred inertatmosphere is an atmosphere of nitrogen.

The reaction between ferrous carbonate and picric acid is preferablyconducted at a temperature between 30° C. and the boiling point of thesolvent medium. More preferably the reaction between ferrous carbonateand picric acid is conducted at a temperature between 60° C. and theboiling point of the solvent medium.

Alternatively, the reaction between ferrous carbonate and picric acidmay be conducted at a temperature between 10° C. and 120° C., and morepreferably between 60° C. and 100° C.

The aliphatic alcohols are preferably straight- or branched-chain C₁ toC₁₂ aliphatic alcohols. More preferred aliphatic alcohols are straight-or branched-chain C₂, C₃ or C₄ aliphatic alcohols. Examples of suitablealcohols include isopropanol, n.butanol and iso-octanol.

The preferred aromatic hydrocarbon solvents are alkylbenzenes ormixtures thereof. Examples include toluene, xylene, or mixtures oftoluene and xylene. Another suitable aromatic hydrocarbon solvent ismarketed under the trade name Solvesso (a trade mark of ExxonCorporation), which comprises a mixture of commercial aromatichydrocarbon fractions.

The present invention also provides a liquid additive for addition tocarbonaceous fuel comprising a ferrous picrate solution produced asherein described, an aromatic solvent, and a straight- or branched-chainaliphatic alcohol.

Picric acid may also be added to the liquid additive if it is consideredthat the ferrous picrate solution does not itself contain sufficientfree picric acid.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The present invention will now be described with reference to thefollowing non-limiting examples.

EXAMPLE 1

Hydrated ferrous sulphate (2.5 g) was dissolved in 100 ml of water atroom temperature in a 250 ml erlenmeyer flask and sparged with nitrogen.About 1 g of "Supercel" (trade mark) filter aid was added to thesolution followed by a 5% solution of sodium carbonate until the liquidbecame alkaline. The liquid was then heated to about 80° C. whilstmaintaining the nitrogen blanket.

The resulting slurry was filtered by suction on a glass fibre filter andthe precipitate washed with hot water until the washings were neutralwhilst maintaining a continuous nitrogen blanket. The precipitate waswashed twice with isopropanol and then once with n.butanol to removewater, maintaining a blanket of nitrogen.

Wet picric acid containing 9 g picric acid on a dry basis and 9 g ofwater was added to 500 ml of xylene in a separating funnel and stirreduntil the picric acid has dissolved. The liquid was allowed to standuntil the aqueous phase had settled to the bottom. The aqueous phase wasrun off and discarded. The solution of picric acid in xylene was thenadded to 400 ml of butanol in a 21 flask and the air above the liquidwas replaced with nitrogen. The filter pad was quickly transferred tothe flask and the resulting mixture stirred and heated to 80° C. whilemaintaining the nitrogen blanket. The mixture became intensely green asferrous picrate formed. After about 4 hours when the reaction wascomplete the nitrogen blanket was discontinued and the mixture wasfiltered on a glass fibre filter and washed briefly with n.butanol. Thefiltrate was retained and made up to 11 with n.butanol. Analysisrevealed that the resulting solution contained 480 mg/l of ferrous iron.

EXAMPLE 2

A fuel additive of the following composition for addition to diesel fuelwas formulated from the above solution.

    ______________________________________                                        Ferrous picrate       0.9    g                                                Picric acid           1.0    g                                                n.Butanol             110    ml                                               Xylene                890    ml                                               ______________________________________                                    

While it has been convenient to describe the invention herein inrelation to particularly preferred embodiments, it is to be appreciatedthat other constructions and arrangements are also considered as fallingwithin the scope of the invention. Various modifications, alterations,variations and/or additions to the constructions and arrangementsdescribed herein are also considered as falling within the scope andambit of the present invention.

I claim:
 1. A process for preparing ferrous picrate comprising reactingunder an inert atmosphere ferrous carbonate substantially free fromferric compounds with a substantially water-free solution of picric acidin a solvent medium selected from an aromatic hydrocarbon solvent, amixture of aromatic hydrocarbon solvents, a straight- or abranched-chain aliphatic alcohol, a mixture of straight-chain aliphaticalcohols, a mixture of branched-chain aliphatic alcohols, a mixture ofstraight- and branched-chain aliphatic alcohols, a mixture ofstraight-chain aliphatic alcohols with aromatic hydrocarbon solvents, amixture of branched-chain aliphatic alcohols with aromatic hydrocarbonsolvents, and a mixture of straight- and branched-chain aliphaticalcohols with aromatic hydrocarbon solvents, to produce a solution offerrous picrate.
 2. A process according to claim 1, wherein the inertatmosphere is continuously maintained during said reaction.
 3. A processaccording to claim 1, wherein the ferrous carbonate is produced byreacting in solution under an inert atmosphere ferrous sulphate withsodium carbonate and in the absence of any added hydroquinone.
 4. Aprocess according to claim 2, wherein the inert atmosphere is anatmosphere of nitrogen.
 5. A process according to claim 3, wherein theinert atmosphere is an atmosphere of nitrogen.
 6. A process according toclaim 1, wherein the reaction between ferrous carbonate and picric acidis conducted at a temperature between 30° C. and the boiling point ofthe solvent medium.
 7. A process according to claim 2, wherein thereaction between ferrous carbonate and picric acid is conducted at atemperature between 30° C. and the boiling point of the solvent medium.8. A process according to claim 3, wherein the reaction between ferrouscarbonate and picric acid is conducted at a temperature between 30° C.and the boiling point of the solvent medium.
 9. A process according toclaim 6, wherein the reaction between ferrous carbonate and picric acidis conducted at a temperature between 60° C. and the boiling point ofthe solvent medium.
 10. A process according to claim 7, wherein thereaction between ferrous carbonate and picric acid is conducted at atemperature between 60° C. and the boiling point of the solvent medium.11. A process according to claim 8, wherein the reaction between ferrouscarbonate and picric acid is conducted at a temperature between 60° C.and the boiling point of the solvent medium.
 12. A process according toclaim 1, wherein the aliphatic alcohol is a straight- or branched-chainC₁ to C₁₂ aliphatic alcohol.
 13. A process according to claim 12,wherein the aliphatic alcohol is a straight- or branched-chain C₂, C₃ orC₄ aliphatic alcohol.
 14. A process according to claim 1, wherein thearomatic hydrocarbon solvent is selected from alkylbenzenes, mixturesthereof and commercial aromatic hydrocarbon fractions.
 15. A processaccording to claim 14, wherein the alkylbenzene is selected fromtoluene, xylene and mixtures thereof.
 16. A process according to claim1, wherein said reaction is conducted in the absence of any addedhydroquinone.
 17. A process for preparing ferrous picrate comprisingreacting under an inert atmosphere ferrous carbonate substantially freefrom ferric compounds with a substantially water-free solution of picricacid in a solvent medium selected from an aromatic hydrocarbon solvent,a mixture of aromatic hydrocarbon solvents, a straight- or abranched-chain aliphatic alcohol, a mixture of straight-chain aliphaticalcohols, a mixture of branched-chain aliphatic alcohols, a mixture ofstraight- and branched-chain aliphatic alcohols, a mixture ofstraight-chain aliphatic alcohols with aromatic hydrocarbon solvents, amixture of branched-chain aliphatic alcohols with aromatic hydrocarbonsolvents, and mixture of straight- and branched-chain aliphatic alcoholswith aromatic hydrocarbon solvents and at a temperature between 10° C.and 120° C., to produce a solution of ferrous picrate.
 18. A processaccording to claim 17, wherein said temperature is between 60° C. and100° C.
 19. A liquid additive for addition to carbonaceous fuelcomprising a ferrous picrate solution produced by a process comprisingreacting under an inert atmosphere ferrous carbonate substantially freefrom ferric compounds with a substantially water-free solution of picricacid in a solvent medium selected from aromatic hydrocarbon solvents,mixtures of aromatic hydrocarbon solvents, straight- or branched-chainaliphatic alcohols, mixtures of straight-chain aliphatic alcohols,mixtures of branched-chain aliphatic alcohols, mixtures of straight- andbranched-chain aliphatic alcohols, mixtures of straight-chain aliphaticalcohols and aromatic hydrocarbon solvents, mixtures of branched-chainaliphatic alcohols with aromatic hydrocarbon solvents, and mixtures ofstraight- and branched-chain aliphatic alcohols with aromatichydrocarbon solvents, to produce a solution of ferrous picrate, anaromatic hydrocarbon solvent, and a solvent medium selected from astraight-chain aliphatic alcohol, a branched-chain aliphatic alcohol,and a mixture of straight- and branched-chain aliphatic alcohols.
 20. Aliquid additive according to claim 19, further comprising added picricacid.
 21. A liquid additive according to claim 19, wherein said reactionis conducted in the absence of any added hydroquinone.